CAIRO — Egyptian election officials said Wednesday that they were postponing the announcement of a winner in last week’s presidential runoff, saying they needed more time to evaluate charges of electoral abuse that could affect who becomes the country’s next leader.

The commission had been expected to confirm a winner on Thursday and, based on a public vote count confirmed in official news media, to have named Mohamed Morsi, of the Muslim Brotherhood.

The surprise delay intensified a power struggle between the Muslim Brotherhood and Egypt’s military rulers. It came just days after the generals who took over upon the ouster of Hosni Mubarak reimposed martial law, shut down the Brotherhood-led Parliament, issued an interim charter slashing the new president’s power and took significant control over the writing of a new constitution.

The new uncertainty about the presidential election results has only heightened the atmosphere of crisis here and raised deep doubts about Egypt’s promised transition to democracy. The generals had promised to hand over power after the election.

Although the vote count appeared to make Mr. Morsi the winner by a margin of nearly one million votes, his opponent, Ahmed Shafik, has also declared himself the winner. A former air force general and Mr. Mubarak’s last prime minister, Mr. Shafik campaigned as a strongman who could keep the Islamists of the Brotherhood in check. His campaign has filed complaints with the election commission charging the Brotherhood with systematic violations of the electoral laws.

“The Most Dangerous 48 Hours in Egyptian History,” declared the headline on Wednesday across the front page of the flagship state newspaper, Al-Ahram.

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Security forces guard the hospital where Hosni Mubarak is being treated.Credit
Adam Ferguson for The New York Times

The delay in announcing the official results came as Egyptians were still grappling with confusion over the health of Mr. Mubarak, 84, the imprisoned former president. The state news agency said Tuesday that Mr. Mubarak was being relocated from a Cairo prison to a military hospital because a stroke and a heart attack had left him near death or even “clinically dead.” Security officials, speaking anonymously, backed up that account. But on Wednesday, a lawyer for Mr. Mubarak said the former leader had fallen in a prison bathroom and was treated for a blood clot in his neck.

Mr. Mubarak was back in the comfort of the military hospital on Wednesday. And Egyptian officials offered no clarification on Wednesday as Egyptian turned their attention back to the looming political crisis.

The election commission said in a statement that it needed more time “to continue viewing the candidates’ appeals.” The commission said it had received more than 400 appeals, including allegations about the printing of premarked ballots, polling places with the number of ballots different from the number of voters, repeat voters and dead voters.

Officials said they expected to confirm the results within days.

Even before the voting was complete, however, the commissioners — a panel of judges who were appointed by Mr. Mubarak — appeared to put their finger on the scale in favor of Mr. Shafik and against Mr. Morsi of the Brotherhood. In television appearances on the final day of the voting, the commissioners floated unconfirmed allegations that could have influenced the vote against the Brotherhood, suggesting that it had infiltrated official printing facilities to produce ballots premarked for Mr. Morsi or that the group might plan violence if he lost.

Brotherhood officials called the delay of the results a power play by the governing military council. In television interviews, Mohamed Beltagy said the generals were holding back the final results to threaten the Brotherhood with the loss of the presidency if the group did not accept the dissolution of the Parliament.

“The delay is damaging, damaging, damaging,” said Morad Mohamed Ali, a spokesman for the Morsi campaign. “The country needs to settle down.”

The Brotherhood and the military council have each been flexing their muscles as the showdown escalates. On Tuesday, the Brotherhood organized a demonstration in Tahrir Square by tens of thousands of its members and others calling for an end to military rule, and by Wednesday it had become a permanent occupation. The group has said it will continue to ramp up a campaign of street protests until the generals back down.

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Soldiers at the Maadi military hospital in Cairo on Wednesday, where former President Hosni Mubarak was transferred after his health deteriorated.Credit
Mohamed Messara/European Pressphoto Agency

The generals, for their part, began deploying tanks and troops on Wednesday at the entrance to Cairo in their own show of force.

Egyptians were left to wonder whether to blame incompetence or some political strategy for the widely divergent health assessments of Mr. Mubarak. All too familiar with dubious reports about Mr. Mubarak’s vigor as president and frailty as a criminal defendant, some speculated about a ruse to lay the groundwork for the former president’s release, or perhaps an even darker plot to withhold confirmation of Mr. Mubarak’s death for later use.

“Maybe it was a decision to delay announcing his death for whatever reason,” said Gamal Abdel Gawad, a researcher at the Al-Ahram Center for Political and Strategic Studies, a state-financed research group. “Certainly there are a lot of issues on the table right now.”

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Yousri Abdel Razeq, a lawyer for Mr. Mubarak, called the descriptions of Mr. Mubarak clinging to life fictional. Mr. Abdel Razeq said that the former president’s transfer from prison to the hospital had been prearranged by legal appeals, and that his main health problem — a blood clot in his neck — was quickly treated with medicine.

“We were surprised at what we can call a media mania in Egypt last night,” Mr. Abdel Razeq said, singling out the official Middle East News Agency for criticism.

Mr. Mubarak’s true condition, including the potential health consequences of even a brief blood clot in his neck, could not be determined. The state news agency said it stood by its report.

By Wednesday night, Egyptians had become as cynical about the reports of Mr. Mubarak’s looming death as they are about the opaque rule of the military council and the convoluted political transition it was steering. One online commentator likened the reports that Mr. Mubarak had been found “clinically dead” to Wednesday’s news that an election commission of Mubarak-appointed judges might put off announcing a winner of the presidential runoff. “If MENA is reporting indefinite postponement of election results,” the blogger Sherief Gaber wrote in an online comment, “it’s likely that results just slipped in the shower & will be out tomorrow.”

Kareem Fahim, Mayy El Sheikh and Liam Stack contributed reporting.

A version of this article appears in print on June 21, 2012, on Page A13 of the New York edition with the headline: As Tension Mounts, Egypt Delays Declaring Winner of Presidential Election. Order Reprints|Today's Paper|Subscribe